This application relates to a specialized sewing machine and method, and particularly to a machine of the type known as a "post" machine, but with a vertically extended post structure, to perform operations such a deck seam.
Such a machine is of unique utility in the automated making of a so-called deck seam around the periphery of a relatively large annular shaped multi-piece fabric member, such as a safety "air bag" for automotive use. Such bags are per se known, and comprise an annular (toroidal shaped) collapsible bag which is secured at its center to a strategic location in a vehicle, such as at the center of a steering wheel, and which includes a quick inflation device responsive to high deceleration of the vehicle to inflate in front of the driver (or passenger) and protect him from injury in an accident. The bags must store in a relatively small space, be dormant for long periods of time, and then function when needed with a high degree of reliability.
The "air" used to inflate these safety bags is in reality a pressurized gas coming from a small high pressure inflator. The fabric of the bag must fit the storage space allotted, inflate to the desired shape under considerable internal pressure, and then release so the protected party will not be trapped in a damaged vehicle by the inflated bag. The fabric is a high strength cloth (usually a closely woven nylon cloth) impregnated with a suitable gas-impervious rubber-like material, and is manufactured by sewing together multiple pieces of such fabric. Obviously the seams at which these fabric parts are joined must also be made with care and precision.
A typical completed air bag has as two of its major parts generally circular front and back panels joined at their periphery by what is known as a deck seam. These panels may have a diameter in the order of 28 to 30 inches (71 to 76 cm.). The front panel is the one which will deploy against the person to be protected, and the back panel is the one anchored to the vehicle via a per se known annular anchoring device of much smaller diameter, secured to the back panel at an opening near its center. It is through this opening that the gas generator inflates the bag during use.
The two panels are stitched preliminarily together around their entire peripheries, by what is usually called a perimeter seam. Next, to form the deck seam, the bands of the panel material outward of this initial seam are then folded over onto one of the panels, usually the front panel, and both outer bands of material are stitched to the panel onto which they are folded. It is important that this second stitched seam be uniformly spaced from the first seam, and be continuous around the two panels, so the resulting closed periphery of the air bag does not leak or burst anywhere around this seam and hamper the deployment and positioning of the bag when it is suddenly needed.
As can be appreciated, the post of the stitching head of a machine making this stitch must reach into the bag interior through the much smaller opening in the back panel. In the meantime, the rest of the bag material must be kept away from the peripheral area and controlled so as not to interfere with the progress of the deck seam operation. Once the dimensions and parameters of the deck seaming job are determined, it is a repetitive operation, thus it can be automated to some extent to assure continued precision of the seaming, and to minimize operator involvement in the control of the bag material.
Post type machines are known, however the usual height of the post, to which the bobbin and feeding dog are mounted, and from which they are driven, is in the order of 6 to 7 inches, which in the case of these larger panels leaves a substantial part of such panels bunched around the bottom of the post and the base of the machine. This in turn presents a handling problem to an operator, and tends to interfere with any attempt to automate, at least partially, this operation.